For example, in an image forming apparatus using an electrophotographic system, such as a facsimile, a printer or a copying machine, a toner is adhered to an electrostatic latent image formed on the surface of a photosensitive member to visualize it, the visualized image is transferred to a sheet or the like and thereafter it is fixed by being heated and pressurized. In terms of achieving high image quality and colorization, as a developer, a so-called two-component developer containing a carrier and a toner is widely used.
In a development system using a two-component developer, a carrier and a toner are agitated and mixed within a development device, and the toner is charged by friction so as to have a predetermined amount. Then, the developer is supplied to a rotating development roller, a magnetic brush is formed on the development roller and the toner is electrically moved to the photosensitive member through the magnetic brush to visualize the electrostatic latent image on the photosensitive member. The carrier after the movement of the toner is left on the development roller, and is mixed again with the toner within the development device. Hence, as the properties of the carrier, a magnetic property for forming the magnetic brush, a charging property for providing a desired charge to the toner and durability in repeated use are required.
As such a carrier, carriers in which various types of ferrite particles are used as carrier core materials and whose surfaces are coated with a resin are generally used. However, a resin coating layer is often separated from the surface of the carrier core material such as by the collision or friction of carriers themselves or carriers and the development device. When the resin coating layer is separated from the carrier core material, a charging property and an electrical property are changed, and thus the image quality is lowered.
Hence, in order to enhance the adhesion of the carrier core material and the resin coating layer, various types of technologies are proposed. For example, patent document 1 proposes a technology in which a layer containing a silane coupling agent is interposed between a carrier core material and a resin coating layer.